Effects of epsilon-polylysine and chitosan functionalization on pulp board properties for food packaging

The production of paper-based food packaging materials is of vital importance as the release of microplastics into aqueous environment and food chain has aroused significant public concern. In this study, antibacterial pulp board was demonstrated by co-spraying chitosan (CS) and epsilon-polylysine (epsilon-PL) on wet sheet and dried to form fibrous pulp board (epsilon-PL-CS). epsilon-PL functionalization showed great antibacterial performance while its hydrophilicity limited its further application for food packaging. Interestingly, epsilon-PL-CS pulp board not only demonstrated excellent antibacterial performance (99.99% against both bacteria Staphylococcus aureus and Escherichia coli), but also maintained high hydrophobicity (ca. 135 degrees) and water resistance due to the positive charge of epsilon-PL and CS as well as penetration of CS into pulp board. In addition, CS functionalization significantly improved the mechanical strength of the pulp board by around 100% (20 MPa). More importantly, the epsilon-PL-CS pulp board could successfully prevent bacteria growth within 15 days at room temperature due to their high hydrophobicity and smooth surface, indicating the long-term stability as packaging materials. Satisfactory strawberry storage stability of epsilon-PL-CS cardboard lunch box provided great application promise for the development of antimicrobial packaging materials.